The invention relates to a brake system having a master brake cylinder embodied as an electrohydraulic booster, as defined herein.
German patent application P 38 42 225.5, which is the same as copending U.S. application Ser. No. 424,648 filed Oct. 20, 1989, describes a brake system by means of which the feeding of servo fluid is controlled by two travel transducers, one of which senses the motion of the piston rod and the other of which senses the motion of the master cylinder piston. From a great number of tests, it is known that the brake characteristic curve, that is, the characteristic curve of pedal force over pedal travel, should be adaptable to a desired deceleration. Slow braking startup requires a long pedal travel, or in other words a soft pedal, so that the deceleration can be metered out properly. In fast braking startup, contrarily, high pressure should be fed in with short pedal travel, and a higher pedal force should be realized by the driver to enable attaining fast deceleration.
Moreover, in many cases a so-called quick speed-change is desired; that is, if the servo circuit fails, it should still be possible to attain the highest possible brake pressure using the master brake cylinder. As a rule, this high brake pressure leads to embodying a master cylinder piston of relatively small diameter. On the other hand, during normal servo operation, the greatest possible braking volume (brake energy) should be available, which once again means that a larger diameter of the master cylinder piston is desirable.